1. Field of the Invention
The present invention relates to compositions that absorb ultraviolet (UV) light and the use of such compositions in contact lenses.
2. Description of the Prior Art
It is well known that sunlight can result in damage to the human eye, especially in connection with the formation of cataracts. The fraction of sunlight of most concern is the long wave or near ultraviolet range, which is characterized by wavelength of 300-400 nanometers (nm). This band of ultraviolet radiation is known to cause damage to the eye by inducing chemical changes in the lens and retina. Though short wavelength light with wave lengths below 300 nm. typically does not reach the earth's surface because of the atmospheric ozone layers, most of the long wave ultraviolet radiation in the 300-400 nm. range is capable of penetrating to the surface of the earth.
The problem of eye damage caused by the penetrating long wave ultraviolet radiation is especially acute in aphakic patients. Aphakic patients have lost their natural lens, which is the primary ultraviolet filter in the eye. Without this natural UV filter, aphakic patients are far more susceptible to the photochemical damage that long range ultraviolet light can induce.
A variety of compositions are known in the art that absorb at least part of the spectrum of ultraviolet light. Examples of such ultraviolet absorbers or blockers are disclosed in Xi et al., "Functional Polymers", Polymer Bulletin 11: 329-335 (1984); Dexter, "UV Stabilizers", Kirk-Othmer Encyclopedia of Chemical Technology 23: 615-627 (3d ed. 1983); Nir et al., "Functional Polymers", Journal of Polymer Science: Polymer Chemistry Edition 20: 2735-2754 (1982); United Kingdom Patent Specification No. 885,986; and U.S. Pat. Nos. 3,399,173 and 3,365,421.
In the context of protecting the human eye, it is known that UV absorbers can be incorporated into spectacles to prevent ultraviolet light from reaching the eye, as disclosed in U.S. Pat. No. 3,171,869. Similarly, it is well known in the art to incorporate ultraviolet blocking compositions into contact lenses, as disclosed in Mandell, Contact Lens Practice: Basic and Advanced (Charles C. Thomas 1965) 234-39; and U.S. Pat. Nos. 2,241,415; 3,189,914; 3,476,499; 4,157,892, 4,304,895; and 4,390,676. Such UV absorbers are typically copolymerized with the base polymer used to manufacture the lens in order to eliminate any possible toxicity or migration problems, as disclosed in U.S. Pat. Nos. 3,186,968; 3,328,491; and 3,340,231. Contact lenses may be formed from such polymers according to various methods well known in the art, such as the spincasting method described in U.S. Pat. No. 3,408,429.
One problem that has arisen in connection with commercial contact lenses containing UV blockers is that they tend to appear yellow. Such yellow appearing contact lenses are not esthetically pleasing to the user and thus present a significant commercial problem. Therefore, there is a need for a UV absorbing composition suitable for use in contact lenses that will not cause the contact lenses to appear yellow and yet will block out as much of the potentially harmful radiation as possible.
An additional problem that has arisen in the curing of materials containing UV absorbing pigments and dyes is that such pigments and dyes adversely affect the curing of such materials with UV radiation. Pappas (ed.), UV Curing: Science and Technology, (Technology Marketing, Stanford 1978), pp. 2-22, 79-95. Therefore, there is a need for a curing method that will avoid such problems in the curing of contact lenses containing UV absorbing compositions.